A liquid crystal display (LCD) is a well known device that uses the light-modulating properties of liquid crystals since liquid crystals, themselves, do not emit light. Nowadays, LCDs occupy a large niche and are used in a wide range of applications, including computer monitors, televisions, instrument panels, video players, gaming devices, clocks, telephones, etc. LCDs have gradually replaced cathode ray tubes (CRTs) and projection-type displays since they generally have a relatively thin sandwiched structure and therefore are more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes. In addition, LCDs are more energy efficient and safer to use, and they can operate in a higher brightness mode than CRTs.
Typically, an LCD comprises an electronically modulated optical device sandwiched from a number of segments filled with liquid crystals and arrayed in front of a light source, which is known as a backlight, or reflector, to produce images in color or monochrome. The most flexible LCDs use an array of small pixels.
A backlight module is one of the main components of any LCD and is the source of illumination used in LCDs. LCDs do not produce light, themselves, and in order to produce an image, they need illumination. This function is accomplished by the backlight module, which illuminates the LCD from the side or back of the display panel.
Typically, a backlight module consists of a lamp and a light-guide panel (LGP). The external light source applied to the backlight module can be properly selected, depending on the size and use of the LCD. The external light source may be a point light source such as a light bulb and a white halogen lamp, a line light source (e.g., a hot cathode or cold cathode fluorescent lamp), or a surface light source (e.g., a light-emitting diode [LED]) formed in an electroluminescent (EL) matrix form.
The LGP, itself, is also an important element of the LCD. An LGP comprises a thin and sandwiched structure, the purpose of which is to provide uniform distribution of light emitted from the backlight lamp under the display structure. An LGP should possess a number of specific properties: the delivery of maximum amount of light from the lamp to the display assembly and the provision of uniform intensity of light over the entire surface of the display. The latter property is important, and hundreds of patents and published patent applications are dedicated to accomplishing this task.
More specifically, some patent publications describe uniformity of backlight illumination achieved by deviation of the LGP from a plane-parallel structure (see, e.g., U.S. Pat. No. 7,845,841 and US Published Patent Application No. 2011/0199786); some patent publications describe uniformity of backlight illumination achieved by modifying methods used for introduction of light into the LGP, e.g., through profiled edges on the panel side (see, e.g., US Patent Application Publication No. 2011/0211368); other publications describe the use of deflectors for diffusion scattering and redistribution of light (see U.S. Pat. Nos. 7,841,730; 8,009,243; and 7,969,532; and US Patent Application Publications Nos. 2011/0205756 and 2011/0199670); and some publications describe uniformity of backlight illumination achieved by dividing the surface of the LGP into separate sections and delivering light to all of these sections so as to provide uniform light intensity in all sections irrespective of local positions and distances from the source of light (see, e.g., US Patent Application Publications Nos. 2011/0194307; 2011/0199559; and 2011/0205453).
The use of lasers for backlighting is known. For example, U.S. Pat. No. 7,508,466 discloses an LCD that includes a planar array of transmissive LCD devices and at least one laser diode device spaced apart from the planar array of LCD devices. At least one laser diode device is configured to illuminate at least one subset of LCD devices in the planar array of LCD devices, so that in operation the laser diode device provides backlighting for the subset of LCD devices.
US Patent Application Publication No. 20110026270 discloses a surface light-source device from which large planar light with uniform light intensity distribution can be obtained from spot-like laser light. The surface light-source device comprises a laser light source for emitting the laser light, an optical system including one or more reflective diffusion members, and an optical waveguide combined with the optical system for converting reflected and diffused laser light into planar light and emitting from a principal plane. The reflective diffusion member converts the laser light emitted from the laser light source into linear light having an arcuate radiation pattern.
US Patent Application Publication No. 20080259247 discloses displays such as LCD panels that are illuminated with frequency-doubled vertically extended cavity surface emitting lasers (VECSELs) as efficient light sources. Visible light from VECSELs are directed to an illuminating panel using optical fibers and/or optical gratings to provide substantially uniform illumination of the illuminating panel. Visible light from the illuminating panel, which can be provided at a particular number of primary wavelengths by the VECSELs, is then used to illuminate the display.
A disadvantage of all LGP devices known to the inventors, including those based on the use of lasers, is their relatively complicated design and low efficiency of illumination.